Casting and sizing method for ferromanganese



Dec. 16, 1969 J. w. FARRELL ET AL 3,483,914

CASTING AND SIZING METHOD FOR FERROMANGANESE Filed April 24, 1967 5 O 5O 6004 mg: @4726 C/m/a.)

United States Patent US. Cl. 16469 4 Claims ABSTRACT OF THE DISCLOSURE Method of casting and sizing high carbon ferromanganese to obtain a substantially uniformly sized product which involves solidifying molten ferromanganese into slabs and cooling the slabs at a predetermined rate in accordance with slab thickness prior to particulating the slabs by shattering impact.

This invention is related to the casting and sizing of ferromanganese alloys. More particularly, the present invention is directed to a method for avoiding the formation of an excess of oversize and undersize high carbon ferromanganese alloy product by controlling the rate at which the alloy is cooled after casting and prior to sizing.

High carbon ferromanganese, which is used as an addition agent in steel making operations is most often sold in particulated form in order to satisfy customer requirements. A size range of about 6 inches to 1 inch has been customary in the past and this was ordinarily obtained by subjecting cast pigs or slabs of ferromanganese to crushing operations, e.g., using a jaw crusher, followed by screening to obtain the required size portion. This procedure involves certain economic penalties which were largely due to the formation of a relatively large amount of fine or undersized particles in the crushing operation which were not saleable and were only suitable for recycling. Moreover, the recoveries of saleable ferromanganese were uncertain on account of inconsistent crush ability characteristics among the ferromanganese castings. The aforementioned difiiculties, together with present day industrial preference for a rather narrow sizing range, has made it important to find an improved method of preparing particulated ferromanganese.

It is therefore an object of the present invention to provide an economical method for obtaining particulated high carbon ferromanganese without the formation of an excessive amount of fine particles.

It is another object of the present invention to provide a method for particulating high carbon ferromanganese by which consistent particle sizing is obtained.

Other objects will be apparent from the following description and claims taken in conjunction with the drawing which shows in- FIGURE 1 a plan view of a particulated slab of ferromanganese which has been cast in accordance with the present invention;

FIGURE 2 a somewhat schematic equipment arrangement suitable for the practice of the present invention; and

FIGURE 3 a graph indicating cooling rates for high carbon ferromanganese castings in accordance with the present invention.

A method for producing particulated ferromanganese in accordance with the present invention broadly comprises:

(1) Providing a mass of molten ferromanganese at a temperature above about 1100 C.;

(2) Pouring the molten ferromanganese into vessels so as to provide slab-shaped pieces of solidified ferromanganese;

(3) Cooling the solidified ferromanganese shapes at a controlled rate in the temperature range of about 900 C. to 400 C. and

(4) Subjecting the cooled solidified ferromanganese to impact sufiicient to cause shattering after solidification and after cooling to below about 200 C.

In the practice of the present invention, molten ferromanganese is conventionally prepared and is of the composition shown in Table A.

TABLE A Percent Mn 7476 Si (man) 1 C 5-8 Fe and incidental impurities Balance The molten ferromanganese, while at a temperature of 1 100 C. or above is cast into an elongate mold, solidified into a slab-shaped form and, in the range of about 900 C. to 400 C. is cooled at a controlled rate depending upon the thickness of the slab, as hereinafter more particularly described. It has been discovered, as part of the present invention, that when high carbon ferromanganese is cooled, after casting, in a certain controlled manner, that a stress pattern is caused to develop in the high carbon ferromanganese casting whereby, when the casting is subsequently subjected to impact, after being cooled to a temperature of 200 C. or less, a highly uniform particulation occurs.

For example, a slab of ferromanganese 20 inches x 10 inches and 4 /2 inches thick Mn, 7% C, 1% Si) cast at a temperature of about 1200 C. and cooled from 900 C. to 400 C. at a rate of about 8.2 C. per minute fractured as shown in FIGURE 1 when dropped, at room temperature, from a height of 3 feet onto a spiked grid. Moreover, essentially the same result is obtained when the slab is fractured by being placed in a tumbling de vice, e.g., of the type described hereinbelow, and tumbled until the slab is shattered. These, and other tests have shown that ferromanganese slabs, when cooled after casting at a particular rate, develop a characteristic stress pattern, which causes the slabs to shatter at temperatures below 200 C. into substantially the same sized particles independently of the means used to provide the shattering impact. That is to say, the ferromanganese slabs are essentially self-sizin in that a slab of given thickness can be shattered by being dropped on grids or flat surfaces, tumbled or hammered while providing essentially the same particle size distribution.

The cooling rate necessary to provide the self-sizing characteristics is related to the thickness of the high carbon ferromanganese slabs and this relationship is shown graphically in FIGURE 3 of the drawing. With reference to figure, in order to obtain self-sizing characteristics in high carbon ferromanganese castings, a cooling rate in the shaded portion of the graph is selected corresponding to the thickness of the ferromanganese slab. In general, with thicker slabs, a slower cooling rate is required. For example, with reference to the graph of FIGURE 3, for a 4 inch thick slab a cooling rate of about 13 to 29 C. per minute in the range of 900 C. to 400 C. will condition the slab so that, upon shattering, about of the resultant particles will pass through a five inch screen and be held on a one inch screen with only about 5% of the particles passing through a one inch screen. Under previous practice, using slabs cast to a size 5 feet by 5 feet by 10 inches thick which were broken into smaller lumps and then reduced further in size by means of a jaw crusher only about 59% of the product was in the desired inch x 1 inch range and the proportion of particles through a one inch screen was about 41%.

With slabs about 2 /2 inches thick, a cooling rate of about 45 to 65 C. per minute is employed in the range of 900 C. to 400 C. and about 85% of the product passed through a three inch screen and was held on a onehalf inch screen. With the previous method as described above it was possible to get only about 70% of the product in the desired range of 3 inch by /2 inch.

By defining fines as particles which will pass through a screen the openings of which are about one-fifth the thickness of the cast slab, the present invention can be said to result in not more than about 5% fines. Also, considering coarse, or oversize particles to be those which will be retained on a screen having an opening 50% or more larger than the thickness of the slab, the method of the present invention enables the production of a product containing not more than 15% total fine and coarse par ticles.

In a particular embodiment of the present invention, and with reference to FIGURE 2, molten high carbon ferromanganese, at a temperature of at least 1100 C. is poured from a ladle 1 into tundish 2 and then into molds 3 which are mounted on casting conveyor 5. The molds can be made of cast iron or steel and are suitably about 20 inches x inches x 5 inches. The molds 3 on casting conveyor 5 are moved by a suitable driving mechanism 4 at a rate such that the ferromanganese is solidified and is at a temperature of about 1100 C. by the time it reaches the end of the casting conveyor 5. Upon reaching the end of casting conveyor 5, the solidified slabs 6 of ferromanganese are ejected from molds 3 and deposited on cooling conveyor 7. To facilitate cooling of the slabs and obtain the cooling rate appropriate to the slabs thickness, air cooling,

for example with fans 9, or water spray cooling, using 1' nozzles 11 can be used. Generally, air cooling is used for the slower cooling rates and with thicker slabs, and water spray cooling is used to obtain faster cooling rates and with thinner slabs. It has been found that while water cooling is effective, it must be in the form of a spray which is applied such that substantially no water collects on the surface of the ferromanganese slabs. That is to say the water must substantially all evaporate on contact with the ferromanganese slabs otherwise penetration of the metal occurs which leads to excessive production of fines.

Upon reaching the end of conveyor 7, the cooled slabs 6 are deposited in a rotating tumbling device 13 in which the slabs are raised by flights 1S and dropped to cause fracture. The resulting particles exit tumbler 13 to screens 17 by which the desired particle sizes are separated from the fine or undersized fraction. With the use of cooling rates in accordance with this invention undersize and oversize fractions are greatly reduced and 85% and more of the particulated product is directly saleable.

The following examples will further illustrate the present invention.

EXAMPLE 1 Using apparatus of the type shown in the drawings, molten ferromanganese alloy having a composition as shown in the Table Ia was poured from a ladle into molds 20 inches x 10 inches x 5 inches which were mounted on a casting conveyor 140 feet long which was driven at a rate of 16 feet per minute.

The ferromanganese solidified in the conveyor molds in slabs 20 inches x 10 inches x 4% inches and was transferred directly from the mold conveyor to a cooling conveyor.

The cooling conveyor was 350 feet in length and transported the ferromanganese at a rate of 3.2 feet per minute so that the ferromanganese was on the cooling conveyor for about 110 minutes. During travel along the cooling conveyor, the ferromanganese was subjected to a cooling treatment so that the temperature of the ferromanganese leaving the cooling conveyor was about 200 C. The cooling rate of the solidified ferromanganese was on the order of 8.2 C. per minute.

Ferromanganese leaving the cooling conveyor was transferred directly to a rotating tumbling apparatus of the type shown in the drawing, whereby the ferromanganese was lifted and dropped about 5 feet between 3 and 5 times before exiting the tumbling apparatus of a screening device.

The sizing of the ferromanganese alloy recovered from the screening device showed the following Table Ib average proportions for 38,000 pounds of alloy.

TABLE Ia: TABLE Ib Mn Held on 5" screen5.2%. Fe (17%) Through 5" screen and held on 1 inch screen9l.8%. C (7%) Through 1 inch screen3.0%. Si (1%).

EXAMPLE 2 Using apparatus of the type shown in the drawing molten ferromanganese alloy having a composition as shown in the Table Hz: was poured from a ladle into molds 20 inches x 10 inches x 5 inches which were mounted on a conveyor feet long which was driven at a rate of 22 feet per minute.

The ferromanganese solidified in the conveyor molds in slabs 19 inches x 9 inches x 2% inches and was transferred directly from the mold conveyor to a cooling conveyor.

The cooling conveyor was 350 feet in length and transported the ferromanganese at a rate of 18 feet per minute so that the ferromanganese was on the cooling conveyor for about 19.4 minutes. During travel along the cooling conveyor, the ferromanganese was subjected to a cooling treatment so that the temperature of the ferromanganese leaving the cooling conveyor was about 200 C. The cooling rate of the solidified ferromanganese was on the order of 46.4 C. per minute.

Ferromanganese leaving the cooling conveyor was transferred directly to a rotating tumbling apparatus of the type shown in the drawing, whereby the ferromanganese was lifted and dropped about 5 feet between 3 and 5 times before exiting the tumbling apparatus of a screening device.

The sizing of the ferromanganese alloy recovered from the screening device showed the following Table III) average proportions for 9,000 pounds of alloy.

TABLE Ila: TABLE III) Mn (75%) Held on 4 inch screen14.8%. Fe (17%) Through 4 inch screen and held C (7%) on A2 inch screen-84.3%. Si (1%) Through /2 inch screen-1.9%.

EXAMPLE 3 Using apparatus of the type shown in the drawing molten ferromanganese alloy having a composition as shown in the Table I was poured from a ladle into molds .10 inches x 10 inches x 5 inches which were mounted on a conveyor 140 feet long which was driven at a rate of 39 feet per minute.

The ferromanganese solidified in the conveyor molds in slabs 18 inches x 8 inches x 1% inches and was transferred directly from the mold conveyor to a cooling conveyor.

The cooling conveyor was 350 feet in length and transported the ferromanganese at a rate of 32.5 feet per minute so that the ferromanganese was on the cooling conveyor for about 10.8 minutes. During travel along the cooling conveyor, the ferromanganese was subjected to a cooling treatment so that the temperature of the ferromanganese leaving the cooling conveyor was about 200 C. The cooling rate of the ferromanganese was on the order of 83 C. per minute.

Ferromanganese leaving the cooling conveyor was transferred directly to a rotating tumbling apparatus of the type shown in the drawing, whereby the ferromanganese was lifted and dropped about 5 feet between 3 and 5 times before exiting the tumbling apparatus of a screening device.

The sizing of the ferromanganese alloy recovered from the screening device showed the following Table IIIb average proportions for 6,000 pounds of alloy.

TABLE IIIa: 7 TABLE HIb Mn 75%) +3 inch-9.8%. Fe 17% -3 inch-HA inch87.4%. c (7%) inch-2.8%. Si 1% The mesh sizes referred to herein are Tyler Standard.

What is claimed is:

1. A method for casting and sizing ferromanganese a1- loys which comprises (1) providing molten ferromanganese at a temperature above 1100 C.

(2) casting the molten ferromanganese to provide individual discrete solidified slabs of a predetermined thickness in the range of about 1 /2 to 4% inches (3) cooling the slabs of ferromanganese in the temperature range of about 900 C. to 400 C. at a rate in the shaded portion of the graph FIGURE 3 corresponding to the thickness of the slab and (4) subjecting the ferromanganese slabs to a shatterti ing impact after the slabs have cooled to below about 200 C.

2. A method in accordance with claim 1 wherein the ferromanganese slab thickness is about 4 /2 inches and the cooling rate in the temperature range of about 900 C. to 400 C. is about 82 C. per minute.

3. A method in accordance with claim 1 wherein the ferromanganese slab thickness is about 2% inches and the cooling rate in the temperature range of about 900 C. to 400 C. is about 464 C. per minute.

4. A method in accordance with claim 1 wherein the ferromanganese slab thickness is about 1% inches, and the cooling rate in the temperature range of about 900 C. to about 400 C. is about 83 C. per minute.

References Cited UNITED STATES PATENTS 3,323,899 6/1967 Forgeng 16494 X 20 3,382,911 5/1968 Malone 164-70 3,429,362 2/ 1969 Tachimoto et al l6470 FOREIGN PATENTS 118,065 1/1944 Australia.

I. SPENCER OVERHOLSER, Primary Examiner JOHN S. BROWN, Assistant Examiner US. Cl. X.R. 

